Very true Rich... That knock you hear is the pistons hitting the valves in the head (top of engine) stop trying to start it! It is making it worse.... and everytime you do you're probably adding £50 to the repair bill. If you've tried starting it there is probably no point trying to re-time the crank/cam. It is very unhealthy and unless it is a very well loved car with a good history it's maybe time to get rid. (head or valves need replacing..... or could even be cheaper to replace the engine)
Sorry for the bad news.
Moz
January 2007